The present invention relates to a novel process for preparing 3,3'-diamino diphenylsulfones.
3,3'-diamino diphenylsulfones are useful as monomers for heat-resistant polymers, agricultural or medical chemicals, intermediates for dyestuffs and the like. Particularly, they are important as raw materials for heat-resistant polyamide or polyimide resins.
In a conventional process, 3,3'-diamino diphenylsulfone is prepared by reduction of 3,3'-dinitrodiphenylsulfone [N. P. Ghatge et al, Angew, Makromol. Chem., 49 (1), 133 (1976); Japanese Patent Kokai Koho No. 56-25150; N. R. Ayyangar et al, Synthesis Communications, 640 (1981), Koristek et al, Czech. No. 158,469; Chem. Abstr., 84 16955 K (1976)]. In this process the starting 3,3'-dinitrodiphenylsulfone is prepared by nitration of diphenylsulfone with a mixed acid [C. A. Buehler et al, J. Org. Chem., 4 262 (1939); J. Lacroix, Bull. Soc. Chim., 35 1436-50 (1924); Chem. Abstr. 19 980] or by nitration and simultaneously oxidation of diphenylsulfide with fuming nitric acid [Baldo Ciocca et al, Gazz Chim. Ital., 76 113-19 (1946); Chem. Abstr., 40 7153 (1946)].
Also, there are known other processes in which 3,3'-dinitrodiphenylsulfone is isolated as by-products in the nitration of benzene in the presence of sulfuric anhydride [W. Alama et al, Biul. Wozskowez Akad. Tech., 13 57-63 (1964); Chem. Abstr., 73 34962 n (1970)] or as by-products in the preparation of m-nitrobenzenesulfonic acid by sulfonation of nitrobenzene [Nazvanova et al, Tr. Khim, Kkim. Tekknol., 178-9 (1969); Chem. Abstr., 73 34962 n (1970)].
However, in the process for the preparation of 3,3'-dinitrodiphenylsulfone starting from diphenylsulfone or diphenylsulfide, since the reaction products obtained by the nitration are a mixture containing isomers, it is necessary for the isolation of 3,3'-dinitrodiphenylsulfone to use a large amount of a solvent and to repeat a recrystallization refining. Therefore, the yield is greatly reduced and complicated operations for recovering the solvent used, for treating residuals and for treating a large amount of waste acids are required.
On the other hand, in the process of by-producing 3,3'-dinitrodiphenylsulfone in the nitration of benzene in the presence of sulfuric anhydride or in the sulfonation of nitrobenzene, there are disadvantages that the yield of end product is low and a necessary amount of supply can not be ensured because the main purpose of that process is not to produce 3,3'-dinitrodiphenylsulfone.
Also, it is known that 3,3'-dinitro-4,4'-dichlorodiphenylsulfone which is one of diphenylsulfone compounds used as the starting material in the present invention is prepared by nitration of 4,4'-dichlorodiphenylsulfone, for example, with an excess of a mixed acid (Ber 40, 640 (1907); Japanese Patent Kokai Koho No. 52-14744).
However, in this process the amount of the mixed acid used is large so that after treatment of waste acids becomes troublesome. Further, it is not easy to isolate the desired compound in a high purity from the reaction product, since the compound tends to take granular forms so as to bear the raw material and the acids therein. It is not easy to refine such compound after the completion of the reaction. It may be proposed to obtain the desired compound in a high purity by isolating said compound by means of filtering immediately after the crystallization from the mixed acid. However, such procedure is troublesome and impractical for commercial production of the desired compound. The process has a further disadvantage from the standpoint of operational easiness and economy in that, as the nitration reaction is exothermal, the reaction must be carried out by adding the raw material stepwise in small doses to the reactor and/or cooling the reactor efficiently.
It has been therefore highly desired to develop a process for commercially producing 3,3'-dinitro-4,4'-dichloro diphenylsulfone by the nitration of 4,4'-dichloro diphenylsulfone in which the reaction heat can be controlled in an easy manner, there is used minimal amount of the mixed acid, the treatments after the reaction can be easily made, and further there can be obtained crystalline 3,3'-dinitro-4,4'-dichloro diphenylsulfone in a high yield and purity.